So I'm stepping things up a little bit...upgrading my current all grain set up to accommodate 10 gallon batches...three young kids, a wife, and a honey-do list that expands exponentially have severely diminished my brew time.

As such, I'm moving from fly to batch sparging and I need to know how long to let my sparge water "rest" in the tun after stirring?

I've spent some looking through existing posts and have found all the other steps, just not a definitive time for the letting the sparge water "rest" prior to vorlaufing.

My first mash is for 1 hour. Vorlauf, drain, refill, stir wait 30 minute and vorlauf/ drain. That's the nuts and bolts of it. There are several good articles on the web on the subject. My efficiency is still in the 80's so I don't see myself ever trying to set up a drip system.

If you have full conversion, testing your first runnings gravity and multiplying it times the total mash water volume (not the first runnings volume, but the strike volume) should calculate to 90-100% efficiency.

What this means is that, after draining the first runnings, the only thing left to do is dilute the liquid that remains on the grain. So, a lot of brewers find that there is no efficiency gain to be had from holding the sparge water on the grain, other than a good stir. I just add the sparge water, stir, vorlauf and drain, myself, and get 87-92% efficiency. Of course that probably adds up to about 10 minutes anyway.

For brewers that tend to get low efficiency, letting the sparge sit can increase efficiency, probably by allowing more time for conversion to occur aided by the elevated temperature. I also suspect that, with a coarse grind it may take a few minutes to completely perfuse the grain. This may be part of the reason grind is so important to efficiency when batch sparging, but again that probably comes down to complete conversion.

You know when someone tells you to do something and it works... you continue to do it. That's where the additional 30 minutes comes in. I do mill my own grains and most likely have complete conversion after the hour. I should only have to add the second addition of water, stir, allow the grain bed to set, and then drain. I do occasionally sparge with additional water to obtain my pre-boil volume. It seems that no matter whose formula I use to obtain my pre-boil, I am either over and have to boil longer or under, and add sparge water to get my pre-boil volume.